If you have these 2 choices only ... 5 calls with 20 Objects each and single call with 100 Objects ..
then selecting 5 json calls with 20 objects is a better choice .. why ?
1 . Time consumed in generating these objects. Time consumed in generating 20 objects in one go will be much more lesser than generating 100 objects.. no matter what business logic is there.
2 . While user is waiting for response.. 5 calls will keep the waiting time to minimum possible showing data progressively .. one by one . Its better to show data progressively instead of showing data at once after a long wait.